Vaulted Ceiling Recipe for Mold?
Customer wants T&G pine car siding as paneling on their vaulted ceiling…no drywall, just R-38 kraft-faced FG batts. FG is installed OK, but there are a few places where gaps in the insulation will bring cold air directly to the back of the pine paneling.
I assume, In most places, the lack of DW would be a code violation…this is a rural MN location with no inspections.
Would you be concerned that this will lead to condensation and mold? Anyone ever put paneling directly over FG w/o drywall?
The backsides of the boards would primed.
No big deal? or No thanks?
Replies
I'd consider adding a poly vapor barrier over the fiberglass, stapled to the rafters, before paneling.
It'll keep the drafts out, and the pine cleaner.
Shep,Would you run poly right over the kraft facing or peel kraft off first?Thanks,BW
You could peel off the kraft, or just slash it with a knife.
No need to peel the Kraft paper off first.
That misconcception comes from the fact that you do not want two vapour barrieers, but that exclusion is that you don't want them on two different sides of a wall to trap water between them. placing theem together skin/skin on same side is just one re-inforcing the other is all.
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I have that exact condition. No mold problems, although there are some drafts. I do have some icing problems also. I installed continuous foam baffles, continuous soffit and ridge vents (on the hip ridges), but that does not vent enough to prevent icing.
If I had to do it over again, I would spray foam the underside of the roof deck. If that is not affordable, consider a layer of rigid insulation attached to framing prior to installation of T&G. At a minimum, skip the kraft faced fiberglass and install a quality vapor barrier and air barrier (look to Henry products i.e. Blueskin?). You might need a substrate to which you can apply the air barrier.
http://www.henry.com/Air___Vapor_Barriers.22.0.html
BMan,Thanks for the input and the Henry link,BW
Maybe not mold but I guarantee condensation. When I was in CO, I would get calls every winter during or right after the cold snaps from people who thought they had leaks springing forth on bright sunny days when it was simply the frost melting off again.
At a minimum, I would staple a good tight plastic over the FG for VB.
Better by far would be Foil faced Thermax insulation board, taped at seams, with strapping over that both to help hold it up and to provide clean nailing for the finish material.
The Insulation panels provide extra insulation, a thermal break at the rafters, and a VB all in one.
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I suggested foamboard and strapping over what is there.Is the pine OK for reducing fire risk with the foam...or would it need gypsum too, before the pine?Thanks for the double vapor barrier clarification,BW
Dunno 'bout that fire thing. I'm sure it is better with rock first. I have only done either/or.Kind of seems like time the fire get through the pine enough to toxic gas the foam, they better be out or dead anyways by then
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That might depend on the foam. The stuff I use is branded "Tuff-R" by Dupont. It carries the specification that it must have at least 1/2" of a non-combustible material (such as wallboard) between it and a living area. One fellow I communicated with claimed to have looked up the materials list and said it resembled rocket fuel.George Patterson
Thanks for the info on Tuff-R. I will use Thermax. Not to many lumber yards carry it any longer. Only found two out of 15 I called who carry it. Thanks Jay
Hey Piffin,I wonder if your response to this question would also work for me. The part about the rigid foam applied with strapping, the foil would act as a cover for the foam and cut back flammability issues, I think. Thought I could install it perpendicular to joist and not have to fit it in between them, sort of like drywall on studs. The alternative would be to spray foam and take left over plywood I have from the concrete foundation forms and cover the foam that way. I appreciate your thoughts.http://forums.taunton.com/tp-breaktime/messages?msg=101335.1and the problem:http://forums.taunton.com/tp-breaktime/messages?msg=101335.9
Edited 2/24/2008 6:35 pm ET by dockelly
I am planning on almost doing the same thing. I am going to nail 2X2 on to the sides of the tops of the 2X6 roof rafters. Then nail a foil faced rigid panel to that. This would create a continuos 1-1/2 are passage from the overhang to the ridge vent. I am then going to spray foam and fill the balance of the rafter cavity. This should give me about an R-24 insulated cavity under the 1-1/2" air space. I might add another 2X2 on the bottom of the roof rafter which would increase the insulation to R-33. Has anyone done anything like this. Jay
the county fire marshall made us coat the interior woodwork in our community hall with a fire retardant varnish.it went on pinkish but dried clear.
in nova scotia we haven't seen kraft-faced batts in 25 yrs.but the vapour barrier gets its own inspection at the same time as the electrical rough-in.taped seams,wrapped top plates,acoustic tile sealant at the floor and wrapped outlet boxes unless you use flanged boxes.oh yeah,s.m.board where joists end at an exterior wall.
did the same thing 3 yrs ago -- FG between the rafters; 1" foam horizontally across the rafters; 2x3's screwed on every other rafter and then 1 3/8's foam insulation in between the 2x3's and beaded T&G siding nailed to the 2x3's -- 3 yrs and no condensation or mold